This invention relates in general to chain coupler links or chain locks, particularly for heavy-duty round steel chains used in underground mining, for instance. The chain link of this invention is of the type which comprises a pair of complementary J-shaped link halves each defining two arms of different lengths and provided at its end with interlockable tongue-and-groove joints and with a spacer piece insertable between the interlocked halves and being provided with projecting noses engageable with arresting recesses formed in the facing wall portions of the longer arms.
In assembling chain coupler links according to the German Standard 22 258 by means of the interposed nose piece, an improper insertion of the nose piece is possible inasmuch as the twin projecting noses of the spacer piece and the corresponding transverse grooves on the two link halves of the chain coupler have the same cross section. This construction permits the insertion of the nose piece in the assigned arresting grooves on the link halves in either of its two possible positions; nevertheless, difficulties may arise when a safety pin is to be driven into an inclined bore passing through the two link halves and the nose piece, because the safety pin can be inserted only in a predetermined position of the component parts of the link. In machining the inclined bore in the link parts minute manufacturing tolerances cannot be avoided, and consequently in the case of an improper insertion of the nose piece between the interlocked link halves a minute overlap of the edges of the bore section will occur. Consequently, this misalignment leads to difficulties in driving the safety pin into the bore.
To avoid this difficulty, the conventional chain links of this kind have employed markings such as center punch marks at suitable points to indicate which nose belongs to a particular transverse groove. Such punch marks, however, are frequently overlooked or their interrelationship is not recognized, particularly under impaired visibility in the dusty environment of mines.